In this contribution, we present an analysis of the experimentally measured magnetic field data from the planar hybrid 40 mm period undulator prototype for the European XFEL, and a simulation of expected radiation properties. Because of manufacturing errors, the magnetic field data include a small horizontal component, as well as some irregularities in its vertical (leading) component. A Fourier harmonics analysis was carried out. It was found that the vertical component of the measured magnetic field includes a sufficiently noticeable (about 6 percent relative to the fundamental) third harmonic component in addition to the fundamental harmonic. The spontaneous radiation properties are simulated from the experimentally measured magnetic field. Relying on computed radiation distributions, the effective magnetic field amplitude, the effective undulator period and deflection parameter are calculated.